Neighboring retinal ganglion cells (RGCs) in the vertebrate retina project to neighboring regions in the optic tectum, forming a topographic map similar to those for other sensory inputs to the nervous system. Such maps are important for faithful transmission of sensory input, and accordingly a firm understanding of their development is important for understanding how we perceive our environment. A large body of evidence supports an instructive role for EphA/ephrinA signaling in establishing the map along the anterior-posterior axis, but a single gradient of repellent activity is insufficient to explain the observed map. I propose to probe previously inaccessible questions using larval zebrafish. Using a novel experimental paradigm, I will observe the retinotectal projection of a single, isolated RGC in chimeric zebrafish to elucidate the role of RGC-RGC competitions during map establishment. Additionally, single-cell knockdown will reveal the role of ephrinAs expression in RGCs, and analysis and identification of the genetic lesion in a mutant with a potentially compressed retinotopic map will further increase our understanding of genetic factors required for retinotopy. [unreadable] [unreadable]